The present invention is directed to a system and method of blood filtration, and more particularly a continuous system and method for the regulation of the rate of filtration of fluid and/or soluble waste from the blood of a patient based on one or more monitored patient parameters.
For various reasons, including illness, injury or surgery, patients may require replacement or supplementation of their natural renal function in order to remove excess fluid or fluids containing dissolved waste products from their blood. Several procedures known for this purpose are dialysis, hemodialysis, hemofiltration, hemodiafiltration and ultrafiltration; another related procedure is plasmapheresis. The specific procedure employed depends upon the needs of the particular patient. For example, dialysis is used to remove soluble waste and solvent from blood; hemofiltration is used to remove plasma water from blood; hemodiafiltration is used to remove both unwanted solute (soluble waste) and plasma water from blood; ultrafiltration is a species of hemofiltration; and plasmapheresis is used to remove blood plasma by means of a plasmapheresis filter. Because the replacement of renal function may affect nutrition, erythropoiesis, calcium-phosphorus balance and solvent and solute clearance from the patient, it is imperative that there be accurate control of the procedure utilized. The accurate control of the rate of removal of intravascular fluid volume is also important to maintain proper fluid balance in the patient and prevent hypotension.
Various systems have been proposed to monitor and control renal replacement procedures. For example, U.S. Pat. No. 4,132,644 discloses a dialysis system in which the weight of dialyzing liquid in a closed liquid container is indicated by a scale. After the dialyzing liquid flows through the dialyzer, the spent liquid is returned to the same container and the weight is again indicated. Since the container receives the original dialyzing liquid plus ultrafiltrate, the amount of ultrafiltrate removed from the patient is equal to the increase in total weight in the container. This system is not driven by a weight measuring device and does not offer precise control of the amount of liquids used in the procedure.
U.S. Pat. No. 4,204,957 discloses an artificial kidney system which utilizes weight measurement to control the supply of substitute fluid to a patient. In this system, the patient""s blood is pumped through a filter and the filtrate from the blood is discharged to a measuring vessel associated with a weighing device. A second measuring vessel containing substitute fluid is associated with a second weighing device and is connected to the purified blood line. By means of a pump, the substitute fluid and the purified blood are pumped back to the patient. The first and second weighing devices are coupled to one another by a measuring system in such a way that a fixed proportion of substitute is supplied to the purified blood stream from the second measuring vessel depending an the weight of the filtrate received in the first measuring vessel. This system does not utilize circulating dialysate fluid in the blood filtration.
U.S. Pat. No. 4,767,399 discloses a system for performing continuous arteriovenous hemofiltration (CAVH). The disclosed system relies upon utilizing a volumetric pump to withdraw a desired amount of fluid from the patient""s blood and return a selected amount of fluid volume to the patient.
U.S. Pat. No. 4,923,598 discloses an apparatus for hemodialysis and hemofiltration which comprises an extracorporeal blood circuit including a dialyzer and/or filter arrangement. The system determines fluid withdrawal per unit time and total amount of fluid withdrawn by utilizing flow sensors in conjunction with an evaluating unit located upstream and downstream of the dialyzer or filter arrangement in the blood circuit.
U.S. Pat. No. 4,728,433 discloses a system for regulating ultrafiltration by differential weighing. The system includes a differential weighing receptacle having an inlet chamber and an outlet chamber which allows a fixed amount of fresh dialysate, by weight, to flow through the hemodialyzer. This system operates in a sequence of weighing cycles during which the amount of ultrafiltrate removed from the blood may be calculated. Additionally, the ultrafiltration rate for each weighing cycle may be calculated. This system provides a mechanism for determining and regulating the amount of ultrafiltrate removed from the blood while delivering dialysate to the patient in alternating fill and drain cycles of the inlet and outlet chambers of the differential weighing receptacle.
The need exists for a multipurpose renal function replacement/supplementation system which is accurate, reliable, capable of continuous, long-term operation, and which can be used effectively on adult, pediatric and neonatal patients.
The present invention is directed to a multipurpose system and method for removal of fluid and/or soluble waste from the blood of a patient: ultrafiltration only, hemodiafiltration, hemodiafiltration and ultrafiltration, and plasmapheresis with or without fluid replacement. The system and method of the present invention can provide reliable, long term operation (5-10 days) with a great degree of accuracy (on the order of +xe2x88x922 grams regardless of the total volume of fluid passing through the system). The system and method of the invention are advantageous because of the multipurpose nature thereof, the repeatability and accuracy of the processes, and the simultaneous, continuous flow of fluids in an extracorporeal blood circuit, while being equally applicable to adult, pediatric and neonatal patients.
As used herein the term xe2x80x9chemofiltrationxe2x80x9d is to be broadly construed to include hemodialysis, hemofiltration, hemodiafiltration, ultrafiltration and plasmapheresis processes. As used herein, the term xe2x80x9cinfusatexe2x80x9d is defined to include dialysate fluid or any other replacement fluids which may be supplied to the patient as a part of the hemofiltration procedures.
In a preferred embodiment, the system of the present invention includes a hemofilter, a blood pump for pumping blood from a patient through the hemofilter and back to the patient, and suitable tubing for carrying the pumped blood to and from the patent. The system further includes a first reservoir for maintaining a supply of infusate, a first weighing means for continuously monitoring the weight of the infusate and generating weight data signals correlated to the monitored weight, and a first pump for pumping the infusate from the first reservoir to the hemofilter or appropriate blood tubing access port. A second reservoir receives drained fluid (e.g., spent infusate or ultrafiltrate, including the fluids and solutes removed from the blood) from the hemofilter, and a second weighing means monitors the weight of the drained fluid and generates weight data signals correlated to the monitored weight. A second pump pumps the drained fluid from the hemofilter to the second reservoir. The system also includes a computerized controller operably connected to the blood pump, the infusate pump, the drain pump and the first and second weighing means.
The controller periodically, but on an ongoing basis during the treatment, interrogates at predetermined intervals the weight data signals that are continuously generated by the first and second weighing means and is designed to determine therefrom the weight of infusate and drained fluid in the first and second reservoirs at the predetermined intervals. The rate of fluid withdrawal from the blood is also determined. The controller compares the infusate and drained fluid weights to corresponding predetermined computed weights in the memory of the controller, and, when necessary, the controller generates control signals which automatically adjust the pumping rates of the infusate and drained fluid pumps in order to achieve a preselected amount of fluid removal from the patient""s blood. Additionally, the controller is programmed to operate the infusate and drained fluid pumps only when the blood pump is operating. Furthermore, the blood pump is operably connected to and is responsive to control signals generated by the controller in response to or independent of the weight data signals to vary the flow rate of the blood through the hemofilter as required to achieve the desired level of fluid removal from the blood.
In an alternative embodiment, the computer controller is, by initial selection of the operator, interfaced with one or more of the various monitoring systems that are operably connected to the patient. These monitoring systems, which are well known in the art, generate and output data signals corresponding to the monitored patient parameters, and the computer controller receives such data signals. During the hemofiltration operation, the interfaced parameters are constantly monitored; however, the controller only responds to specific parameter data that corresponds to the patient parameters selected by the operator. The patient parameters which may be monitored and interfaced with the computer controller include the following: arterial pressure, central venous pressure, pulmonary arterial pressure, mean arterial pressure, capillary wedge pressure, systemic vascular resistance, cardiac output, O2 saturation (mixed venous or arterial), blood pressure, heart rate, patient weight, external infusion rates, and hematocrit. Numerous of these parameters may be monitored and corresponding output data signals generated in known manner utilizing an indwelling intravenous or intra-arterial catheter. The remaining parameters are monitored and data signals are generated by means well known in the art. The operator will select one or more of the above parameters to interface with the controller which will then periodically, but on an ongoing basis during treatment, interrogate at predetermined intervals the parameter data signals that are continuously generated by the interfaced monitoring system(s). The controller then evaluates the parameter data and in response thereto, when necessary, the controller generates control signals which automatically adjust the pumping rates of the infusate, drained fluid and blood pumps so as to achieve a preselected amount of fluid removal from the patient""s blood.
It will be appreciated that the system of the present invention may utilize a combination of monitoring and responding to the infusate and drained fluid weight data signals, as described in connection with the first embodiment hereinabove, along with one or more of the other patient parameters interfaced to the controller.
By way of specific examples, in connection with monitoring the patient""s weight, the computer controller may be interfaced with a bed scale which provides continuous values for the patient""s weight. In response to the overall patient weight data signals, the computer controller may control the infusate and/or drained fluid pumps to achieve a predesigned protocol for decreasing or increasing the patient""s weight over time. The change in patient""s weight (by increase or decrease) can be accomplished in either a linear or non-linear (such as curvilinear) manner with respect to time by appropriate pump control. Similarly, the computer may be interfaced with a continuous read-out device of the patient""s O2 saturation and the controller will receive, evaluate and respond to the O2 saturation data by controlling the infusate, drained fluid and blood pumping rates accordingly.
In connection with all of the above-described monitored parameters, the computer controller will receive data signals corresponding and relating to each particular selected parameter from an appropriate signal generating device or source operably connected to the patient. The controller will then, after periodic interrogation, compare the interrogated values with predetermined desired values and will automatically make the appropriate, predetermined changes in the infusate, drained fluid and blood pumping rates in response to the monitored signals. Furthermore, more than one of the above-referenced parameters can be continuously monitored simultaneously and the computer may be programmed with a hierarchy to consider one or more specific parameters rather than others and will respond with the appropriate and desired adjustments in infusate, drained fluid and blood pumping rates based on those selected parameters.
The computer controller is designed and programmed to adjust the pumping rates (pump speed) of the infusate, drained fluid and blood pumps so as to provide a linear response or a non-linear (curvilinear) response to the observed changes in the selected monitored parameters. In this regard, xe2x80x9clinearxe2x80x9d is defined to mean a fixed, non-exponential change, and xe2x80x9cnon-linearxe2x80x9d or xe2x80x9ccurvilinearxe2x80x9d means anything other than linear. The selection of linear versus non-linear response profile is made by the operator of the system depending on the needs of the patient. For example, in certain situations it may be desirable to have an initially fast fluid removal rate that decreases over time. In that case a curvilinear or exponential response would be utilized. In other circumstances, consistent or constant fluid removal over time is desired, and so a linear response profile is selected. It is further contemplated that at the election of the operator the computer controller may combine linear and curvilinear response signals so as to tailor the pump rates to achieve a desired response profile. For example, a non-linear initial response period for fast initial fluid removal, followed by a linear response period for ongoing fluid removal at a consistent rate.
In yet another alternative embodiment, the computer controller receives data signals from one or more patient infusion pumps that are otherwise independent of the hemofiltration system. These infusion pumps are used for infusion to the patient of intravenous fluids, medications, parenteral nutrition and/or blood products. By monitoring the data output from the independent infusion pumps, the extraneous total fluid volume per unit time may be ascertained. The controller will then, as required, change the pumping rates of the system infusate, drained fluid and blood pumps, as necessary, so as to alter the ultrafiltration rate and/or infusate fluid rate automatically in response to changes in intravenous fluid therapy. This facilitates independent patient management while hemofiltration is being performed. Proper coordination of the controller with the independent infusion pumps allows the desired or targeted fluid removal goals by hemofiltration to be achieved automatically in concordance with ongoing intravenous fluid therapy.
In a preferred embodiment of the method of the present invention, blood from a patient is pumped through a hemofilter and a supply of infusate, which is maintained in a first reservoir, is pumped from the first reservoir through the hemofilter, countercurrent to the blood. The weight of infusate in the first reservoir is continuously monitored and data signals correlated to that weight are generated. Drained fluid (e.g., spent infusate) is pumped from the hemofilter and is received in a second reservoir. The weight of the drained fluid in the second reservoir is continuously monitored and weight data signals correlated thereto are generated. The signals correlated to the weight of infusate and drained fluid are interrogated at regular intervals (for example every minute) by a system controller and are compared to corresponding predetermined computed weights in the memory of the controller. The controller determines the amount and rate of fluid withdrawal from the patient""s blood. If those values differ from preselected, preprogrammed desired values, the controller generates control signals which independently adjust the pumping rates of the infusate and drained fluid pumps so as to achieve the desired amount of fluid removal. The control signals may also control the blood pumping rate.
In an alternative embodiment of the method of the present invention, independent of or in addition to the infusate and drained fluid weight monitoring and pump control, the computer controller may be interfaced with one or more of the previously discussed monitoring systems. In this embodiment, the controller will receive, evaluate and respond to the selected patient parameter data by generating appropriate, responsive control signals by which the infusate, drained fluid and blood pumping rates are controlled to achieve the desired amount of fluid removal. This may be accomplished in combination with or independent of the infusate and drained fluid weight monitoring.
The advantages of the system and method of the present invention are achieved at least in part due to the continuous monitoring and periodic interrogation of the fluid weights, and other selected patient parameters, and the adjustment of fluid pumping rates in response thereto, including the blood pumping rate, so as to achieve ideal or nearly ideal fluid removal and replacement if necessary from a patient""s blood. Further features and advantages of the system and apparatus of the present invention will become apparent with reference to the Figure and the detailed description which follows.